Finned heat exchanger



1962 w. c. JOHNSON 3,067,492

FINNED HEAT EXCHANGEZR Filed April 12, 1960 2 Sheets-Sheet 1 INVENTOR.WALLACE C. JOHNSQN BY Ms Dec. 11, 1962 w. c. JOHNSON 3,067,492

FINNED HEAT EXCHANGER Filed April 12, 1960 2 Sheets-Sheet 2 JNVENTOR.WALLACE C JOHNSON A TTOR/VEVS United States Patent @fifice 3,067,492Fatented Dec. 11, 1962 3,067,492 FINNED HEAT EXCHAN GER Wallace C.Johnson, I-llatnden, Conn, assignor to Olin Mathieson ChemicalCorporation, East Alton, 111., a corporation of Virginia Filed Apr. 12,1960, Ser. No. 21,690 8 Claims. (Cl. 29157.3)

This invention relates to hollow sheet metal articles and moreparticularly to a method of manufacturing hollow articles, such as heatexchangers and the like, of iheet metal having integral fins extendingexternally there- In the fabrication of hollow articles such asrefrigerator panels, condensers and the like of sheet metal, it isdesirable that such structures be provided with external iins forfacilitating the transmission or dissipation of heat. Such heat transferfins are usually brazed or soldered on the structure posing a difficultmanufacture problem particularly where an article is of flat or oblongsheet metal, thin walled tubing. This involves not only a complicatedand time consuming operation, but in addition is an expensive procedurewhich frequently fails to result in a rigid and efficient joint betweenthe elements. Such a procedure or operation is further complicated bythe need for making good contact between the tube sheet and the fins forproper heat conduction as well as securely assembling the parts. Despiteprecautions taken for the efficiency and operation of the resultantproduct, the brazed or soldered joint is, nevertheless, of reduced heatexchange efiiciency for lack of unimpeded heat transfer through thejoint.

Accordingly, it is an object of this invention to provide a novelprocess for the manufacture of finned heat exchangers eliminatingdisadvantages of the prior art.

Another object of this invention is to provide a novel method for themanufacture of a heat exchanger having an extended heat transfersurface.

A still another object of this invention is to provide a novel methodfor the manufacture of finned heat exchangers.

A further object of this invention is to provide a novel method for themanufacture of thin walled relatively fiat metal tube sheet having aplurality of integral fins extending from an external surface of thetube sheet.

A still further object of this invention is to provide a novel methodfor a substantially simultaneous manufacture of a plurality of saidstructures having an extended heat transfer surface.

Other objects and advantages will become more apparent from thefollowing description and drawings in which:

FIGURE 1 is a perspective View partly in section illustrating oneembodiment of this invention and depicting a plurality of elements insuperposed relationship to each other; 7

FIGURE 2 is an exaggerated cross-sectional view depicting the elementsof FIGURE 1 after superimposition upon each other in accordance with oneembodiment of this invention;

FIGURE 3 is a partial view in perspective of one of the elementsemployed in the preceding figures;

FIGURE 4 is a partial view illustrating cross-section of the embodimentsof FIGURE 1 upon unification of the various elements illustrated inFIGURES l and 2;

FIGURE 5 is a partial view of a cross-section of the embodiments of thepreceding figures in a subsequent operation;

FIGURE 6 is a partial cross-sectional view depicting an assembly ofelements for illustrating another embodiment of this invention;

FIGURE 7 is a partial cross-sectional view illustrating the assembly ofelements of FIGURE 6 after unification to each other;

FIGURE 8 is a partial cross-sectional view illustrating the structure ofFIGURE 7 after a subsequent operation;

FIGURE 9 is a partial cross-sectional view illustrating the structure ofFIGURE 8 after a still further operational step;

FIGURE 10 is an exploded view in perspective illustrating a variationfor some of the elements that may be employed in the assembly of theembodiment depicted in FIGURE 6; and

FIGURE 11 is a partial view in perspective illustrating the elements ofFIGURE 10 after unification to each other.

Broadly, in accordance with this invention a plurality of fin strips arearranged and assembled in spatial relationship with each other betweentwo adjacent panelswhose interiors are partially laminated in a patternof an inflatable system of passageways, or between other similar panelstructures, as for example prior to their fabrication frorn superposedsheets with stop-weld material disposed between them in a patterndefining the desired system of tubular passages. These fin strips aredisposed in two layers between the pair of adjacent superposed panelswith the strips in each of the layers being arranged in spaced andparallel relationship with each other in their respective layers andwith the strips in each of the layers being in staggered and overlappingrelationship with the strips in the other of said layers. Prior toassembly the strips are coated with a weld-inhibiting or stop-weldmaterial, such as graphite in water class, in the portions thereof whichare to form the desired fin portions, and to thus separate them fromeach other and from adjacent panels. Generally, this coating of stopweldmaterial will be applied to all the surfaces of said strips except inthe portions of these strips defined between adjacent edges of adjacentstrips overlapping there- After assembly the various elements may besuitably secured together, as by spot-welding, to prevent relativemovement between them and then subjected to a pressure reduction, as bypressure welding between a pair of mill rolls, to unify all adjacentsurfaces of the elements not separated by the stop-weld material inaccordance with conventional practices. Typical conditions with whichthe panel of this invention is unified or welded are set forth in thewell known process of fabricating hollow panels, such as refrigeratorheat exchangers and the like, disclosed in the patent to Grenell, U.S.No. 2,690,002, granted on September 28, 1954.

Upon unification of the various elements the strips in one layer becomeunified or integrated to one of the panels adjacent the opposite layer,of strips, with the unwelded portion of the strips being in interlockedrelation with each other. The adjacent panels are then separated, suchas by spacing them from each other sufficiently to disengage theoverlapping or interlocked unwelded portions of the strips while forcingthese strips to bend away from panel surfaces to which they have welded.Thus, each strip forms a dual fin structure welded to the panel andextending outwardly at an angle therefrom. Separation of the panel maybe accomplished by any conventional means, either mechanical or by fluidpressure, whereafter the inflatable laminations within each panel maythen be inflated into a panel containing the desired tubularconfiguration.

In accordance with one aspect of this invention the fins may extend fromonly one side of the panel by limiting the number of panels in theirsuperposed relationship to two with the assemblage of fin stripsadjacent only one side of each panel. In another aspect of thisinvention the fins may protrude from both sides of the panel inassemblages of three or more superposed panels where one or more of thepanels has an assemblage of strips adjacent each side thereof. In onearrangement the fins may be disposed in any portion and extend in anydirection on the panel, for example in portions of the panel betweenadjacent passages, however, in a preferred arrangement of fins, thepassages carry the fins. This preferred arrangement may be obtained byapplication of the. invention to panels having a system of passagescomprised of a plurality of inflatable passages in parallel and spacedrelationship to each other with passages in one of the superposed panelsdisposed in spaced and staggered relationship to similar passages in theadjacent panel over which it is superposed with the assembly of finstrips arranged so that the portion of these strips, in one of thelayers, devoid of any coating of stop-weld material will be adjacent andopposite one of the two said panels which is adjacent the other of saidlayers of strips, and in corresponding areas of this panel opposite thepassages.

More specifically by reference to the drawings, one embodiment of thisinvention comprises a plurality of elongated insert or fin strips 1 and2 having pressure weldable surfaces which are coated with a stop-weldmaterial 3 in the portion of the strips desired to form the fins on theultimate article. As illustrated in FIGURE 3 one of the strips 1, whichmay be identical to strip 2, has all of its surfaces coated withstop-weld 3 so as to leave a band 4 devoid of stop-Weld materialdefining the portion of. the strip which will be unified, as by welding,to the heat exchanger on which the desired fins are to be formed.

Subsequent to the coating with stop-weld material the strips aredisposed between a pair of superposed hollow metal blanks 5- and 6:which have their interior laminated in a predetermined pattern 7 and 8,respectively, defining an. inflatable system of tubular passages. Thesestrips are arranged. so that strips 1 will be disposed in spacedrelationship with each other in one layer adjacent blank 5 whereasstrips 2 will be arranged in spaced relationship with each otheradjacent blank 6. In addition, the strips in one layer, as for examplestrips 1, will be also disposed so that each of the bands of the stripsdevoid of stop-weld material will be opposite and facing the blank, forexample blank 6, adjacent the strips in the other layer, for example thelayer containing strips 2. In addition, the strips in each layer, as forexample 1, further arranged in staggered and overlapping relationshipwith the strips in the other layer, as for example strips 2, with eachof the strips overlapping theother strips in their portions coated withstop-weld material leaving the band on each strip devoid of stop-Weldmaterial free for welding to their respective blanks opposite this band.

One method ofobtaining blanks 5 and 6 employed in this embodiment is bythe aforementioned patent to Grenell whereina pattern of stop-Weldmaterial is interposed between two metal sheets in a pattern defining acorresponding and desired system of passageways after which the sheetsare selectively Welded, as by pressure welding between mill rolls, intheir adjacent areas not separated by the stop-Weld material. Althoughthe pattern of laminations 7 employed may be any simple or complicatedinflatable pattern of passages, preferably this pattern of internallaminations 7 is comprised of a pinrality of inflatable passages 13 ineach blank, as illustratedin blank 5, disposed in parallel and spacedrelationship to each other with each parallel passage 13 of one blank,as for example 5, being disposed in parallel and staggered relationshipto similar parallel passages 13 in theo-therblank, as for example 6.Also, the passages 13 of one blank are preferably disposed opposite theband of a respective strip devoid of stop-weld material which strip isin a layer of strips adjacent the other panel.

The strips may be arranged between blanks 5 and 6 by." positioning thetwo layers of strips on one of the blanks, suchas- 6, in the arrangementabove specified and then superimposing the other blank on thearrangement l changer is to be put.

of strips. In order to facilitate the assembly of blanks and strips forsubsequent separation by fluid pressure any convenient configuration ofedge bars 9 and 10 are disposed adjacent the peripheral edges of theblanks in a manner, permitting their unification to blanks 5 and 6 as bythe absence of stop-weld material on these bars. In order to adapt theassembly to subsequent injection of fiuid pressure the scams orinterfaces between the edge bars may be suitably welded together.However, if the ultimate separation of the unified assembly of stripsand blanks is to be separated by mechanical means, the edge bars 9 and10 may be coated with a stop-weld material to prevent their welding toany of the blanks or strips with their subsequent removal. However,where the assembly of strips and blanks is to be separated by fluidpressure, this assembly is adapted for such separation by applying acoating of stop-weld material 11 to a portion of one of the edge bars 10in communicating relationship with a face of one of the strips, either'lor 2, coated with stop-weld material, as for example, a face 12indicated in FIGURE 2. This coating 11 of stop-Weld material adapts theassembly, after unification, for injection of a fluid pressureinternally of the assembly.

Although in this embodiment all the strips 1 and 2 have been illustratedas being of equal Width, it is to be understood that the widths may bevaried depending on the configurations desired in the fin structure ofthe heat exchanger either by personal preference or by conditionsdictated by the application to which the heat ex- In any even, ifdesired, after as sembly of the components various elements in themanner described above, the assembly is appropriately secured togetherby any conventional manner as by spotwelding so as to prevent relativemovement of the elements in preparation for subsequent unh ication ofthe elements together.

Although only a pair of blanks 5 and 6 were employed in this embodiment,it is to be understood that any greater number of blanks may be employedwith the aforesaid arrangement of strips inserted between adjacentblanks. Where as in this embodiment only a pair of blanks 5 and 6 areemployed the ultimate structure will have fins extending from only oneface of the blank. However, where more than two blanks, such as threeare used, with the aforesaid arrangement of strips between adjacentpanels, as will be understood, the blank or blanks having the abovearrangement of strips disposed adjacent each of its opposite faces willhave, in the final article, fins extending from both opposite facesthereof Also, any variety of metals may be employed depending not onlyon economic considerations but particularly upon the specificapplications to which the ultimate panel is to be put. Accordingly, thearticle of this invention may be made from aluminum alloys, copperalloys, titanium, zirconium, steel or similar alloys. lso the blanks andthe strips employed may be of any combination of metals for any desiredapplication. Similarly any stop-weld material capable of preventingunification of the various elements between their adjacent surfaces maybe substituted for the specific stop-Weld material described above.

Subsequent to securing the various elements together against relativemovement between them, the assembly of elements is then ready forunification of the various elements in accordance with conventionalpractices, for example, the elements may be Welded together in theiradjacent areas not separated by stop-weld material by pressure Weldingin accordance with the conditions disclosed in the method of theaforementioned patent to Grenell. In accordance With the methoddescribed in this patent the assembly of elements is heated to pres surewelding temperatures and immediately rolled between a pair of mill rollswhich pressure weld together all adjacent surfaces not separated by thestop-weld material resulting in a substantially complete erasure of theinterfaces between the blanks and the strips by interdispersion of thegrains between the adjacent surfaces. The resultant juncture is usuallycharacterized by a tensile strength equal to that of the other seamlessregions of the structure. As will be understood, the amount of reductionrequired to effect pressure welding will vary with the particularcombination of metal and the physical properties thereof. Generally, areduction of the order of 35% or more will accomplish pressure weldingof adjacent surfaces not separated by the stop-weld material. However,it will be understood that lower or higher percent reductions may besuflicient or required with different metals and/ or differenttemperatures from room temperature on up.

By reference to the exaggerated drawing of FIGURE 4 it can be seen thatthe portions of the strips devoid of stop-weld material in one layerbecame welded, upon pressure welding, to corresponding portions of ablank adjacent the strips in the other layer of said strips becomingintergrated therewith. In contrast, the adjacent surfaces between thevarious strips and blanks separated by the stop-weld material result inlaminations 14 extending in a continuous unbroken lamination 14coextending between all the unwelded portion between the strips and theblanks, thus, defining parallel rows of fins on each blank interlockedwith each other.

After pressure welding the blanks 5 and 6, with their attendant finsunified thereto, are then separated by spacing them in any convenientmanner, either mechanically or with fluid pressure, sufiiciently todisengage the overlapping and interlocked unwelded portions of thestrips whereupon each strip welded to its respective panel becomesdisengaged from the strips of the other panel while forcing each otheraway from their respective panel surfaces. Upon separation each stripforms a dual fin structure welded to its respective panel and extendingoutwardly at an angle therefrom. Where the panel is to be distendedmechanically, as for example, by a vacuum applied on the externalsurfaces of each blank with subsequent spacing, the edge bars 9 and 10may be removed either as a result of being unwelded due to an initialcoating of stop-weld material on all their surfaces, or these bars maybe removed by trimming the edges of the blank followed by separation ofthe blanks.

However, a preferred method of separation is with fluid pressure eitherby free expansion or between spaced rigid surfaces. In employing thislatter means, the welded assembly of elements is placed between a pairof spaced rigid platens and 16, and a suitable fluid is injected intothe unwelded portions between the two adjacent blanks through theportion of one of the bars 10 to which the coating of stop-weld material11 was applied. Thus, a fluid 17 is injected under su'flicient pressurewithin the welded assembly of elements so as to force the two blanksaway from each other against the platens which leaves their externalsurfaces flat. During such inflation the two layer multiplicity ofinserts bonded to their respective blanks are forced to bend anddisengage from each other to form the desired configuration of finsextending at an angle from their respective blanks. Subsequent to thisinflation operation, the inflated assembly of elements may then beremoved from between the platens, the edges of the assembly trimmed toseparate the finned blanks into separate and individual structuresfollowed by expansion of the internal pattern of tubular laminationscontained within each blank in accordance with conventional practices.

Alternately and preferably the pattern of internal laminations of eachblank is expanded prior to trimming while the expanded assembly ofelements is disposed between platens 15 and 16. In this alternate mannerthe fluid 17, under pressure, is then sealed between the blanks 5 and 6,and the platens 15 and 16 spaced further apart a distance equal to theamount of expansion desired, in the internal pattern of laminations, outof the faces of the blank. Thereafter, the fluid pressure are releasedand the blank withdrawn from the platens and trimmed along its edges toform individual finned and inflated panels adaptable for use as heatexchangers, such as refrigerator evaporator panels, condensors, radiatorstructures and the like.

In accordance with another embodiment of this invention and by referenceto a specific example, four sheets of 1100 type aluminum alloy, inaccordance with the Aluminum Associations standard designations, each 10inches wide, 12 inches long and 0.125 inch thick were arranged into twosuperposed adjacent pairs of sheets 18 and 19, each pair 18 and 19having interposed between a stop-weld material disposed in a patterncorresponding to the desired configuration of tubular passages andcomprising bands of stop-weld material 20 corresponding to a pluralityof parallel inflatable passages in spaced relationship to each other.This pattern of stop weld material defining the plurality of parallelpassages was, as in the previous embodiment, arranged so that the bands20 of stop-weld material between one pair of sheets 18 and 19 were inparallel and staggered relationship to the bands 20 of stop-weldmaterial disposed between the other pair of sheets 18 and 19.

As illustrated in FIGURE 6, the two pairs of sheets are disposed so thatsheets 18 are in the interior of the four sheet pack. Arranged betweenthe two sheets 18, of the two pairs, is an arrangement of insert or finstrips disposed in two layers therebetween, with each layer comprised ofrelatively wide strips 21 with each adjacent pair interspersed withrelatively narrower strips 22. Strips 21 in each layer are arranged inparallel and overlapping relationship with strips 21 of the other layerof strips with all adjacent surfaces between strips 21, of both layers,and the surfaces of the internal sheets 18 adjacent to them separatedwith stop-weld material 23. This arrangement places the strips 21 ineach layer of strips in spaced relationship to each other with thestrips 22 disposed between adjacent strips 21 in each layer. Thesestrips 22 are also adjacent the portions 24 of strips 21 in the otherlayer which are not overlapped by other strips 21 and which are alsodevoid of stop-weld material. Thus, all surfaces which are adjacent tostrips 22 are not separated by any stop-weld material, for example theadjacent and opposing surfaces of inner sheet 18 and the portion 24 ofthe surface of strip 21 not coated with stop-weld material.

In forming the above assembly each pair of sheets 18 and 19 with thepattern of stop-weld material can be suitably secured to each other byany suitable manner, such as by spot-welding at the corners, to preventrelative movement between them during assembly of the above arrangementof strips 21 and 22 into their respective layers. Subsequent theretolayer of strips formed alternately of strips 21 and 22 are layed on topof one of the pairs of sheets 18 and 19 with strips 21 disposed parallelwith and between the portions of the pair of sheets opposite the bandsof stop-weld 20, contained between this pair of sheets 18 and 19. Strips22 are then placed between adjacent strips 21 and disposed so as to beparallel with and over the bands of stop-weld 20, contained between thispair of sheets 18 and 19. A similar and second layer of strips 22arranged alternately with each other are placed on top of the firstlayer in parallel relationship therewith. The arrangement of strips 21in the second layer is such that they are in staggered and overlappingrelationship with strips 21 in the first layer. In order to fill theunlapped portion at the most lateral strips 21, an edge or side bar 25is employed to hold the double layer of strips in closed contact witheach other. In the specific example, each of the strips 21 was of theabove referred-to 1100 type aluminum alloy twelve inches long, one inchwide and 0.060 inch in thickness, and each of strips 22 was the samealloy, length and thickness but differing in that they were inch widecorresponding to aoezasa the width of the portions of strips 21 notoverlapped by adjacent strips 21 in the other layer.

Subsequent to the arrangement of strips, the other pair of sheets 18 and19, with the pattern Zt of stop-weld material between them and securedagainst relative movement, was then superimposed on the abovearrangement of strips 21 and 22 to form a six-ply or sheet pack teninches wide, twelve inches long and about 0.625 inch in thickness. Theinterposition of stop-weld material between all adjacent surfaces, ofstrips 21, and the adjacent surfaces of inner-sheets 18 adjacent themwere obtained by coating strips 21, prior to their arrangement in thestructure, with a stop-weld material so as to fully cover all theirsurfaces except one face which is partially covered with stop-'weldmaterial so as to leave an uncoated area 4 inch wide down the center ofthe strip on top of which is placed the narrow inch wide insert havingno portion of its surfaces coated with stop-weld material.

After assembly of the six-ply or sheet pack, it was suitably welded atconvenient intervals to prevent relative iovement between them and thepack was then heated for forty-five minutes at 1000 F. followed by hotrolling it between a pair of mill rolls to a 65% reduction, in twopasses, resulting in an elongated structure of 0.220 inch in thickness.This was followed by a cold reduction of 30% so as to obtain a finishgauge in the structure of 0.150 inch.

As will be noted in FIGURE 7, upon pressure welding the adjacentsurfaces, strips 22 of each layer are welded to corresponding portionsof sheets 18 and to the adjacent uncoated portions of strip 21 in theother layer whereas each pair of adjacent sheets 13 and 19 are weldedtogether in the areas not separated by the patterns of a stop-weldmaterial. The portions within the pressure welded structure preventedfrom welding by the stop-weld material comprised a system of internallaminations corresponding to the patterns of stopweld materialinterposed between each pair of adjacent sheets 18 and 19, to provide aninflatable system of tubular passages including a plurality ofinflatable tubular passages 27. In addition, the coating of stop-Weldmaterial employed with strips 21 forms a continuous and unbrokenlamination defining the division between an interlocked arrangement ofthe fins welded or unified to each pair of integrated sheets 18 and 19.

Subsequent to the cold reduction the pressure unified assembly at finalgauge was placed between a pair of rigid platens 2? and 3d spaced oneinch apart. A fluid 31 under a pressure of 500 psi. was then injectedinto the laminations 23, defined between the unwelded interior portionsof the structure defined between the innersheets 18 to expand andseparate the pairs of unified sheets 18 and 19 away from each other andagainst the rigid platen adjacent their external faces. Duringseparation these two layers of multiple inserts which were welded, inaccordance with the above, alternately to the inner surfaces of the twopairs of unified sheets 18 and 19, were forced to expand, in contactwith each other to an elevated position of 45 with the edges passing,although not shown, beyond contact with each other forming. Thisseparation of the panels 34 and 35 with its attendant unlocking of theinterwoven fins, Welded to their respective panels, spatially forms thestrips into a corresponding arrangement of fins 36 and 37 Welded topanels 34 and 35 respectively.

Subsequently, the pressure was then sealed between the pressure unifiedsheets 13 and 19 and the rigid platens 29 and 3t? spaced slightlyfurther apart a distance equal to the expansion desired in theinflatable system of tubular passages. Thereafter, a fluid 32 undersufiicient pressure was injected into the system of inflatable tubularpassages to expand them into contact against the rigid platens 29 and3t) adjacent each external face of the structure. This expansion formedthe corresponding systern of tubular passages including a plurality ofparallel spaced passages 33 in each panel on which the fins were formed.During expansion, which involves elongation of the metal defining thetubular passages, the structure is restrained on its outer surfaces bythe rigid platens,

and restrained on the inner finned surface by the original inflatingfluid employed for separating the panels and which is sealed betweenthem. Upon completion of the expansion the fluid pressure is releasedand the Water drained from within the expanded structure which is thenremoved from between the platens. Thereafter, the edges of the inflatedstructure were trimmed as along line 38 to allow the panels to beremoved from each other into separate and individual panels with theirrespective fins welded thereon. In accordance with this specific examplein this embodiment, the fin structure had a 0.015 inch thicknesscorresponding to a tubular wall thickness, inflated, of 0.060 inch inthickness which is about one-half the thickness of the tubular wall. Aswill be understood the fins can be made thinner or thicker as desired inaccordance with the requirements of various applications.

in a variation of this embodiment FIGURES 10 and 11 illustrate a mannerin which the fin strips 22 of one layer may be unified to a strip 21prior to placement in the arrangement between adjacent pairs of sheets18 and 19. As illustrated in FIGURE 10, strip 22 may be superimposed onstrip 21 and the two strips suitably secured or unified together to forma combined strip 39, by spot-welding or pressure Welding. This strip 39is then coated with stop-weld material 41 on all surfaces, except on theface 4! of strip 22 opposite the face welded on strip 21, prior to itsplacement in the arrangement of strips disposed between the two adjacentpairs of sheets 18 and 19.

In addition, although a simple internally laminated panel has beendescribed, it is to be also understood that the invention is equallyapplicable to sheets having other patterns of internal laminationseither in the single stratum or plural stratums, or in otherconfigurations, as for example the panel disclosed in the patent toAdams, US. 2,766,514, granted on October 16, 1956.

Although the invention has been described with reference to specificembodiments, materials and details, various modifications and changes,within the scope of this invention, will be apparent to one skilled inthe art, and are contemplated to be embraced within the invention.

What is claimed is:

l. A method for making hollow panels with integral fins extendingtherefrom with each of said panels being ductile and having internallydisposed therein an unjoined interior portion extending in a patterndefining a desired system of tubular passages adapted to contain afluid, said method comprising superposing said panels on each other witha plurality of parallel and ductile fin strips disposed in two layersbetween two adjacent panels and with each of said strips separated fromeach other and from said adjacent panels by a stratum of stop-weldmaterial disposed adjacent the portions of said strips desired to formsaid fins, said strips in each of said layers being arranged in spacedrelationship with each other in their respective layers and with saidstrips in one of said layers arranged in staggered and overlappingrelationship with said strips in the other of said layers, and saidstratum comprising areas devoid of said stop-weld material between thesurfaces of each of said strips and the surfaces of said two panels inthe portions of said strips defined between adjacent edges of adjacentstrips overlapping thereon; pressure welding the assembly of said panelsand said strips in their adjacent areas not separated by said stop-Weldmaterial whereby the strips in each one of said layers are welded tocorresponding portions of one of said two panels adjacent the strips inthe other of said layers; and separating said panels by spacing themfrom each other sufiiciently to disengage the overlapping unweldedportions of said strips whereby each of said layers of strips welded .toone of said two panels forces the strips of the other of said layersfrom their respective panels at an angle therefrom to form said fins.

2. A method for making hollow panels with integral fins extendingtherefrom with each of said panels being ductile and having internallydisposed therein an unjoined interior portion extending in a patterndefining a desired system of tubular passages adapted to contain a fluidand comprised of a plurality of said passages disposed in parallel andspaced relationship to each other, said method comprising superposingsaid panels on each other with a plurality of parallel and ductile finstrips disposed in two layers between two adjacent panels and with eachof said strips separated from each other and from said two panels by astratum of stop-weld material disposed adjacent the portions of saidstrips desired to form said fins, said plurality of passages of one ofsaid two panels'being disposed in parallel and staggered relationship tosaid plurality of passages in the other of said two panels, and saidstrips in each of said layers being arranged in spaced relationship witheach other in their respective layers with said strips in each of saidlayers arranged in staggered and overlapping relationship with saidstrips in the other of said layers, and said stratum comprising areasdevoid of said stop-weld material between the surfaces of each of saidstrips and the surfaces of said two panels in the portions of saidstrips defined between adjacent edges of adjacent strips overlappingthereon with said areas of said strips in each of said layers oppositethe portion of said stratum devoid of said stopweld material beingadjacent and opposite one of said two panels adjacent the other of saidlayers in corresponding areas of said one panel opposite said pluralityof passages; pressure Welding the assembly of said panel and strips intheir adjacent areas not separated by said stopweld material whereby thestrips in each of said layers are welded to corresponding portions ofone of said two panels adjacent the strips in the other of said layers;and separating said panels by spacing them from each other suflicientlyto disengage the overlapping unwelded portions of said strips wherebyone of said layers of strips welded to one of said two panels forces thestrips of the other of said layers from their respective panels at anangle therefrom to form said fins.

3. A method for making hollow panels with integral fins extendingtherefrom with each of said panels having internally disposed therein anunjoined interior portion extending in a pattern defining a desiredsystem of tubular passages adapted to contain a fluid, said methodcomprising forming a structure of a plurality of superposed metal sheetsfrom at least a pair of adjacent first sheets and a second sheetadjacent the external face of each of first sheets, a plurality ofparallel and ductile fin strips disposed in two layers between saidfirst sheets with a stratum of stop-weld material separating adjacentsurfaces of said first and second sheets and said strips, said stop-weldmaterial being disposed between adjacent first and second sheets in apattern corresponding to a desired system of tubular passages anddisposed adjacent the portions of said strips desired to form said fins,and said strips in each of said layers being arranged in spacedrelationship with each other in their respective layers with said stripsin one of said layers arranged in staggered and overlapping relationshipwith said strips in the other of said layers wherein a stratum stop-weldmaterial adjacent said strips comprising areas devoid of said materialbetween the surfaces of each of said strips in the portions of saidstrips defined between adjacent edges of the strips overlapping thereon;pressure welding the assembly of said sheets and said strips in theiradjacent areas not separated by said stop-weld material whereby adjacentfirst and second sheets form said panels and said strips in each of saidlayers are welded to corresponding portions of one of said first sheetsadjacent the strips in the other of said ii) layers; and separating saidpanels by spacing them from each other sufficiently to disengage theoverlapping unwelded portions of said strips whereby one of said layersof strips welded to one of said first panels forces the strips of theother of said layers from their respective panels at an angle therefromto form said fins.

4. The method of claim 3 wherein said pattern of stop- Weld materialcomprises a plurality of said passages disposed in parallel and spacedrelationship to each other with said plurality of passages between oneof said first sheets and the second sheet adjacent thereto are disposedin parallel and staggered relationship to said plurality of passagesbetween the other of said first sheets and the second sheet adjacentthereto, and said areas devoid of said material arranged opposite one ofsaid first sheets adjacent the other of said layers in correspondingareas of said one first sheet opposite said plurality of passages.

5. A method for making hollow panels with integral fins extendingtherefrom with each of said panels being ductile and having internallydisposed therein an unjoined interior portion extending in a patterndefining a desired system of tubular passages adapted to contain afluid, said method comprising superposing said panels on each other witha plurality of parallel and ductile fin strips disposed between twoadjacent panels with said strips in each of said layers comprising aplurality of first fin strips and a plurality of second fin strips andsaid first strips in both said layers being separated from each otherand from said two panels by a stratum of stop-weld material, said firststrips in each of said layers being arranged in spaced relationship witheach other in their respective layers and in staggered and overlappingrelationship with said first strips in the other of said layers withsaid second strips being disposed in portions of each of said layersbetween adjacent first strips therein and adjacent a first strip in theother of said layers overlapped by said adjacent first strips and withthe said stratum in said portions comprising areas devoid of saidstop-weld material; pressure welding the assembly of said panels andsaid strips in their adjacent areas not separated by said stop-weldmaterial whereby said first strips in each of said layers are welded toone of said two panels adjacent thereto and to a second strip adjacentthereto in the other of said layers; and separating said panels byspacing them from each other sufliciently to disengage the overlappingunwelded portions of said second strips whereby the portion of saidstrips welded to one of said two panels disengages from and forces theother of said strips welded to the other of said panels away from theirrespective panels to form said fins.

6. The method of claim 5 wherein said system of tubular passages iscomprised of a plurality of said passages disposed in parallel andspaced relationship to each other with said plurality of passages in oneof said two panels disposed in parallel and staggered relationship tosaid plurality of passages of the other of said two panels, and saidsecond strips being arranged opposite corresponding areas of one of saidpanels adjacent thereto opposite said plurality of passages.

7. A method for making hollow panels with integral fins extendingtherefrom with each of said panels having internally disposed therein anunjoined interior portion extending in :a pattern defining a desiredsystem of tubular passages adapted to contain a fluid, said methodcomprising forming a structure of a plurality of ductile metal sheetsfrom at least a pair of adjacent first sheets and a second sheetadjacent the external face of each of said first sheets, a plurality ofparallel and ductile fin strips disposed in the two layers between saidfirst sheets with said strips in each of said layers comprised of aplurality of first fin strips and a plurality of second fin strips, anda stratum of stop-weld material separating adjacent surfaces of saidfirst sheets, second sheets and said first strips with said stop-weldmaterial being disposed between adjacent first and second sheets with apattern corresponding spa/3492 1 1 to desired system of tubular passagesand disposed between each of said first strips and said first sheetsadjacent the portions of first strips desired to form said fins, andsaid first strips in each of said layers being arranged in spacedrelationship with each other in their respective layers and in staggeredand overlapping relationship with said first strips in the other of saidlayers with said second strips disposed in portions of each of saidlayers between adjacent first strips therein and adjacent a first stripin the other of said layers overlapped by adjacent first strips and withsaid stratum in said portions comprising areas devoid of said stop-weldmaterial; pressure welding the assembly of said sheets and said stripsin their adjacent areas not separated by said stop-weld material wherebyadjacent first and second sheets form said panels and said second stripsin each of said layers are welded to corresponding portions of one ofsaid first sheets and to a second strip adjacent thereto in the other ofsaid layers; and separating said panels by spacing them from each other'sufiiciently to disengage the overlapping unwelded portions of saidsecond strips whereby the portion of said 12 strips welded to oneof'said two panels disengages from and forces the other of said stripswelded to the other of said panels away from their respective panels toform said fins.

8. The method of claim 7 wherein said system or tubular passages iscomprised of a plurality of said passages disposed in parallel andspaced relationship to each other with said plurality of passages in oneof said two panels disposed in parallel and staggered relationship tosaid plurality of passages of the other of said two panels, and saidsecond strip being arranged opposite corresponding areas of one of saidpanels adjacent thereto opposite said plurality of passages.

References Cited in the file of this patent UNITED STATES PATENTS2,212,481 Sendzirnir Aug. 20, 1940 2,498,275 Johnson Feb. 21, 19502,851,770 Fromson Sept. 16, 1958 2,912,075 Pfistershammer Nov. 10, 1959

